Following the fast development of high technology, computers have become more and more important in our daily life. Therefore, using a keyboard for data entry has become a part of routine works in our daily life. When users press the key switch, the keycap is closely attached to the rubber dome and the gas within the rubber dome is exhausted. However, a vacuum may be produced within the key switch, and in turn, the movement of the key switch will be affected. Thus, it is desired to provide a key switch with an exhaust structure so that the gas within the keyboard can exhaust freely and the formation of the vacuum can be effectively eliminated during the operation of the keyboard.